Regularly changing the password for your Office 365 account and entering it in to the settings on your mobile device and desktop e-mail program is required to maintain access to your account – http://community.office365.com/en-us/w/exchange/1728.aspx (“To avoid any lapse in connectivity between your Office 365 account and your mobile devices or desktop e-mail programs, we recommend that you create a recurring appointment to remind you to periodically change the password on your Office 365 account and on your mobile device or desktop e-mail program.”)